To install a GPS navigation system in your dashboard, disconnect the car's battery, and remove the necessary dashboard panels. Connect the GPS wiring, and mount the GPS to the dash.
First, you need to disconnect the car's battery, so the GPS equipment doesn't get damaged if there is a short. Remove the dashboard panels surrounding the car's stereo system using a panel tool.
Install the GPS unit right after connecting the wiring. You can run the necessary wiring on your own or use a wire harness. The wire harness contains connections for the cars wiring, so you don't have to worry about running wiring throughout the car.
If you choose not to use the wire harness, you have to connect the GPS equipment to the speakers and the battery. Some GPS systems must have speed sensors attached to them, so the GPS knows how fast the car is traveling, as well as the reverse signal to tell the car if it's moving in reverse, which allows the car to track its direction accurately. The GPS should only be attached to the car battery once all the other wiring is complete.
Finally, mount the GPS unit to the dashboard, and attach all the panels. Start the car, and test if the GPS system works.